Since semiconductor nanocrystals [quantum dots (QDs)] have been adopted as a new class of fluorescent labels, many studies have indicated a broad range of potential applications using QDs as new probes in vivo and in vitro imaging. Because of QDs long lifetimes (10s of ns) compared to organic fluorophores (1-5 ns), QDs can be used as new fluorescence lifetime imaging probes to reduce cells and tissue's autofluorescence background (2-4 ns). This NIH SBIR project will focus on developing a new generation of cadmium-free, water-soluble multicolor QDs for lifetime imaging to eliminate the autofluorescence for in vitro QD-imaging of biomarkers in tumor cells and tissue sections. A key feature of this new approach is to tune QD emission color by doping the QD core with a third element rather than changing the particle sizes. This kind of new type doped QDs should bring wide interest in the applications of fluorescence labeling due to long lifetime emissions from doped ion itself and possible high emission efficiency by QDs as donors and doped ions as accepters. The doped core/shell QDs would be converted to water soluble and biocompatible for the potential biomedical applications in the field of real-time imaging. [unreadable] [unreadable] [unreadable]